Method and System for Generating a Computed Tomography Image

1. A method of generating a computed tomography image comprising: acquiring a first plurality of projections at a first energy level; acquiring a second plurality of projections at a second energy level; reconstructing an image from the first plurality of projections; generating a synthesized projection from the image that corresponds to one of the second plurality of projections; comparing the synthesized projection to said one of the second plurality of projections; and modifying the image to form an updated image based on said comparing the synthesized projection to said one of the second plurality of projections.

2. The method of claim 1 , wherein the first energy level comprises a higher energy level than the second energy level.

3. The method of claim 1 , wherein the first energy level comprises a lower energy level than the second energy level.

4. The method of claim 1 , wherein said comparing the synthesized projection to said one of the second plurality of projections comprises calculating a difference between the synthesized projection and said one of the second plurality of projections.

5. The method of claim 1 , wherein said modifying the image comprises applying an update function that varies based on a CT number.

6. The method of claim 1 , further comprising displaying the updated image.

7. The method of claim 1 , wherein the updated image represents the second energy level.

8. The method of claim 1 , wherein the first plurality of projections contains more than 5 times the number of projections as the second plurality of projections.

9. The method of claim 1 , wherein the second plurality of projections comprises two or more projections separated by a common angle.

10. The method of claim 1 , wherein the second plurality of projections comprises 4 projections separated by 45 degrees.

11. A method of generating a computed tomography image comprising: acquiring a first plurality of projections at a first energy level; acquiring a second plurality of projections at a second energy level; reconstructing an image from the first plurality of projections; generating a plurality of synthesized projections from the image, each of the plurality of synthesized projections corresponding to one of the second plurality of projections; comparing each of the plurality of synthesized projections to the corresponding one of the second plurality of projections; and modifying the image to form an updated image based on said comparing each of the plurality of synthesized projections to the corresponding one of the second plurality of projections.

12. The method of claim 11 , wherein said modifying the image comprises applying an update function that varies based on a CT number.

13. The method of claim 11 , wherein said comparing comprises calculating a difference between each of the plurality of synthesized projections and the corresponding one of the second plurality of projections.

14. A method of generating a computed tomography image comprising: acquiring a first plurality of projections of an object at a first energy level; acquiring a second plurality of projections of the object at a second energy level; reconstructing an image of the object at the first energy level from the first plurality of projections; modifying the image to generate an updated image of the object, wherein the updated image represents the object at the second energy level.

15. The method of claim 14 , wherein said modifying the image comprises iteratively modifying the image.

16. The method of claim 14 , wherein iteratively modifying the image comprises four or more iterations.

17. The method of claim 14 , further comprising acquiring a third plurality of projections at a third energy level.

18. The method of claim 17 , further comprising modifying the image to generate a second updated image, wherein the second updated image represents the third energy level.

19. A computed tomography imaging system comprising; a gantry; an x-ray source attached to the gantry; a table adapted to translate with respect to the gantry; and a processor in electrical communication with the gantry, the x-ray source, and the table, wherein the processor is configured to: acquire a first plurality of projections at a first energy level; acquire a second plurality of projections at a second energy level; reconstruct an image from the first plurality of projections; generate a synthesized projection from the image that corresponds to one of the second plurality of projections; determine a difference between the synthesized projection and said one of the second plurality of projections; and generate an updated image by modifying the first image based on the difference between the synthesized projection and said one of the second plurality of projections.

20. The computed tomography imaging system of claim 19 , wherein the processor is further configured to display the updated image.

21. The computed tomography imaging system of claim 19 , wherein the first energy level exceeds the second energy level.

22. The computed tomography imaging system of claim 19 , wherein the second energy level exceeds the first energy level.

23. The computed tomography imaging system of claim 19 , wherein the updated image represents the second energy level.

24. The computed tomography imaging system of claim 19 , wherein the processor is further configured to apply an update function that varies based on a CT number of a voxel in the image.